The present disclosure relates generally to a mechanical chuck with a retaining ring. Specifically, the present disclosure relates to systems and methods that provide an air zone at an inner diameter of a retaining ring within a chuck assembly.
Many conventional systems use a chuck assembly for Chemical Mechanical Polishing (CMP). The polishing head is on top, and it has a circular shape in the horizontal plane. Around the circumference of the polishing head is a retaining ring. A round semiconductor wafer is loaded into the chuck by using a vacuum to hold the wafer to the polishing head, where the wafer sits within the retaining ring. The chuck system is then closed by contacting the exposed surface of the wafer to a polishing pad on a platen. The wafer is then moved relative to the polishing pad to perform polishing.
In some embodiments the retaining ring is constructed of plastic. In conventional CMP systems, there is about 1 mm of clearance between the side of the wafer and the side of the retaining ring. In other words, the retaining ring is just a little larger in its inner diameter than is the wafer, and the purpose of this clearance is to facilitate loading of the wafer into the polishing head.
As a result of the clearance, the wafer moves relative to the retaining ring during polishing. Such movement leads to contact stress during CMP processes that causes pitting on the inner circumference of the retaining ring. If byproduct builds up in the pits, it can result in increased scratch defect possibility, increased bevel damage possibility, and lower yield. Accordingly, a more effective technique for CMP is called for.